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D.C. Hood, L. Xu, T. Grippo, J. Chen, V.C. Greenstein, J.M. Liebmann, R. Ritch; Factors Involved in the Failure of the Photopic Negative Response (PhNR) and Pattern Electroretinograms (PERG) to Detect Glaucomatous Damage in Some Patients . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3751.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The pattern electroretinogram (PERG) can be normal in patients with confirmed glaucomatous damage . To examine the factors involved, various functional measures were compared. Methods: PERGs, photopic negative responses (PhNR), multifocal visual evoked potentials (mfVEP), and Humphrey 24–2 visual fields (HVF) were obtained from each eye of 12 patients and 17 controls. PERGs and PhNRs were recorded with DTL electrodes and the Espion system (Diagnosys). The mfVEPs were obtained using the VERIS system (EDI) and analyzed with custom software as previously described . The eyes were classified as "more" or "less affected" based upon the MD of the HVF. Results: All of the more affected eyes had abnormal HVF (abnormal GHT and an abnormal cluster of points) and an abnormal mfVEP (cluster). Three of these eyes had both normal PERG and PhNR responses. These three also had abnormal HRT results. Six of the less affected eyes had both abnormal HVFs and abnormal mfVEPs. Two of these eyes had normal PERG and PhNR responses and a third a normal PhNR. While the mfVEP amplitude of the more affected eye was consistently smaller than that of the better eye, the amplitudes of the PERG and PhNR responses tended to be similar in amplitude. Consistent with this finding, the relative amplitudes of the mfVEP from the two eyes correlated better with the difference in MD (HVF) than did the PhNR or PERG. Further, the monocular mfVEP amplitude, but not the PERG or PhNR amplitude, showed a good correlation with MD field loss. Conclusions: Both PERG and PhNR can be normal in patients with glaucomatous defects confirmed on mfVEP, HVF and HRT. As the PERG and PhNR produce similar results, various factors (e.g. optical correction) particular to the PERG are eliminated as the cause of the false negatives. However, both the PERG and PhNR lack topographical information and, unlike the mfVEP, the PERG and PhNR are not reduced to the noise level by glaucomatous damage. On the other hand, the results are consistent with the view that both measures are sensitive to early damage [3,4]. 1. Xu et al (ARVO, 2005) 2.Hood & Greenstein (2003) PRER 3. Porciatti & Ventura (2004) Ophthal 4. Viswanathan et al (2001) IOVS..
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